1. Field of the Invention
The present invention relates to an apparatus and a method for on-line decomposition of a hydrogen peroxide solution for use in the fabrication of a semiconductor device and, more particularly, to an apparatus and a method for decomposing the hydrogen peroxide solution on-line and then injecting the decomposed products into an analytical instrument to thereby analyze the micro contaminants in the hydrogen peroxide solution.
2. Discussion of the Related Art
As the size of a semiconductor device is reduced further and further, and thus becomes more densely integrated, micro contaminants existing in the constituent layers of the semiconductor device exhibit a greater effect on the device characteristics. Consequently, there is a continuing emphasis to remove the micro contaminants throughout the fabrication process of the semiconductor device.
Generally, a wet cleaning process is the most widely used procedure to reduce or eliminate semiconductor wafer contamination. However, the chemicals used in the wet cleaning process must also have a high degree of purity so as to prevent a wafer from being re-contaminated by the wet cleaning process itself. Therefore, it is necessary to perform a quantitative and qualitative analysis of the micro contaminants contained in the chemicals prior to their use. The micro contaminants can include heavy metals such as iron (Fe), aluminum (Al), copper (Cu), and the like, and ions of sodium (Na.sup.+), ammonium (NH.sub.4.sup.+), nitrate (NO.sub.3.sup.-), chloride (Cl.sup.-), and the like. In order to analyze these contaminants, analytical apparatus and methods are used, for example, a graphite reactor atomic absorption spectrometer (GFAAS), an induced coupling plasma mass spectroscope (ICP-MS) and an ion-exchange chromatograpy (IC).
Hydrogen peroxide solution is one chemical that is widely used in wet cleaning processes for semiconductor devices. However, the hydrogen peroxide readily oxidizes, making it difficult for the analyzer to perform a successful analysis because the oxidation may cause damage to the analytical instruments. In addition, the oxidation could also result in changes in viscosity of the cleaning solution, and the generation of bubbles when analyzing a highly concentrated hydrogen peroxide solution in the above analytical instruments.
Accordingly, to perform an efficient analysis of the hydrogen peroxide solution in an analytical instrument, it is necessary to reduce the concentration of hydrogen peroxide. Different methods are used to reduce the concentration of the hydrogen peroxide. In a so-called dilution method, the hydrogen peroxide solution is diluted with distilled water. In another so-called decomposition method, the hydrogen peroxide contained in the hydrogen peroxide solution is decomposed into water and oxygen gas.
The dilution method is easy and simple to carry out, but it has a disadvantage in that the detection capacity of the instrument may deteriorate as a result of the frequent dilution of the sample. Accordingly, it is not suitable for a method of reducing the concentration of hydrogen peroxide which requires a detection capacity for contaminants on the order of a hundred parts per trillion (ppt) and less.
In an attempt to solve this problem, another technique has been developed whereby the hydrogen peroxide solution is concentrated in an analytical column before an analysis is carried out. In this technique, the hydrogen peroxide solution is first diluted to a designated point so that it does not damage the analytical column, and is then again concentrated on line in the column so as to minimize the deterioration of detection sensitivity. But, this method is not applicable to performing infinitesimal quantitative analysis because it requires another apparatus and additional concentration steps. As a result, the analysis time is prolonged and the possible contamination of the sample is increased due to the extended sample flow path.
On the other hand, a decomposition method, which is carried out using a platinum catalyst, has merit in that the detection capacity is not lowered because there is no need to dilute the sample. In such a platinum catalyst decomposition method, a platinum wire or platinum net is used as a heterogeneous catalyst in the hydrogen peroxide solution. The platinum catalyst can be reused because the catalyst does not dissolve in the hydrogen peroxide solution, and an aqueous solution is produced according to the decomposition of hydrogen peroxide.
However, this method also suffers some drawbacks in that it takes a long time to decompose the sample, raising other possible contamination problems during the decomposition. Also, the contaminants contained within the sample may be chemically changed due to the heat generated by the decomposition of the hydrogen peroxide solution.
In another decomposition method for hydrogen peroxide using ultraviolet (UV) rays, the hydrogen peroxide solution contained in a quartz container is irradiated by the ultraviolet (UV) rays. One benefit of the UV method is that there is no need to add any materials to the hydrogen peroxide solution. However, the UV method also presents problems, perhaps more serious than the platinum catalyst decomposition method, in that it takes a much longer time for decomposition and causes much greater chemical changes in the contaminants in the solution.
An additional disadvantage of both of the above-described platinum catalyst and UV decomposition methods is that each is carried out in a batch process, and therefore the apparatus for decomposition cannot be connected on-line to the analytical instruments. As such, it is difficult to perform an on-line, real-time automatic analysis of the sample.
Accordingly, a need exists for an on-line decomposition apparatus and method for reducing the concentration of hydrogen peroxide contained in the hydrogen peroxide solution so as to perform an on-line, real-time automatic analysis of micro contaminants in an analytical instrument.